Cellulose-based biomass may be hydrolyzed to sugars and the sugars may then be used for the production of yeasts. The yeasts can then be used as animal food stuffs or the sugars applied to produce useful chemicals such as ethanol and furfural.
According to one known process a weak acid solution is applied as reagent to the biomass to extract hemi-cellulose and improve the permeability of the cellulose. The hemi-cellulose may be further hydrolyzed to hexoses and pentoses. One of the costs in this, or any biomass digester system, is the amount of reagent solution employed.
Biomass is generally fibrous and of low density. It is necessary to contact the biomass with the activating solution in order to initiate the desired reaction. The high percentage of voids in biomass has previously required the use of large amounts of reagents to effect the desired reaction.
It is also known to apply a vacuum to material to be digested, prior to application of a reagent. This procedure has, however, been directed to de-aerating the digestible material itself so as to facilitate more through penetration of the reagent into the substance of the biomass itself. References to this type of procedure may be found in U.S. Pat. Nos. 4,057,461; 3,532,594; 3,278,367; 3,259,538; 3,076,501 and 2,694,632.
It is also known to effect a consolidation of silage through vacuum compression, as part of a process for effecting the anaerobic digestion of silige. c.f., "Effect on Intake and Production of Dairy Cows of Feeding Three High-Moisture Siliges Having Different Fermentation Characteristics" by R. J. Lancaster et al, 1974 New Zealand Journal of Experimental Agriculture, vol. 2, 389-92; and "High-Moisture Silage from Mixed Pasture Herbage as a Feed for Lactating Dairy Cows" by J. B. Hutton et al, New Zealand Journal of Agricultural Research (1971) vol. 14, 393-405; and "Quality Storage Losses of Silages Made in Bunkers, Stacks, and by Vacuum Compression" by R. J. Lancaster, New Zealand Journal of Agricultural Research (1968) vol. 11, p. 63-79. See also French patents 1,442,390 and 1,049,415.
The application of vacuum in the prior art has not been resorted to as a means for effecting compaction of the digestible biomass in conjunction with the application of reagents to thereby improve the wetting of the biomass and effect a reduction of the quantity of reagent required.
It is further known to agitate a liquid or slurry, such as sewage sludge in a digester, by periodically inflating and deflating a bladder immersed therein, c.f., U.K. patent 2,056,870 issued Mar. 25, 1981, for an invention by R. C. Baskerville et al. However, no use is known of the application of such a bladder to the agitation of a biomass matrix, in conjunction with the vacuum compaction and chemical treatment of such biomass with reagents. Further, special advantages may be obtained in choosing the location of such bladders.
The prior art also discloses in U.S. Pat. No. 4,176,203 a process for progressively distributing an alkaline liquid across the top surface of a mass of ligno-cellulosic material. This progressive distribution is achieved mechanically by moving the liquid distributing member reciprocally across the upper surface of the biomass. No attempt is made to control the downward displacement over time of the applied reagent, in progressive stages which proceed in conjuction with the exhaustion of the digestion process in consecutive layers of the biomass.
The present invention relates to a structure for containing biomass for digestion. More particularly it provides a means by which:
(1) biomass may be more effectively wetted
(2) reduced quantities of reagents may be used to effect various stages of the digestion process,
(3) valuable products may be recovered at the end of the process;
(4) biomass may be sterilized for long term storage; and
(5) biomass may be sterilized and then exposed to preferred species of micr-organisms.
The latter aspects of the invention are useful in providing a means for controlling the yeast-reaction, and in some applications, arresting the decay of biomatter in the digester.
In many countries crops producing waste biomass are brought-in over a short period e.g. 1-3 months, during the year. Where such biomass may be converted to animal feed, storage becomes a problem. Animals need to consume feed continuously, 12 months a year. In the tropics it is particularly difficult to store biomass for long periods as head and moisture contribute to the rapid rotting of vegetable matter.
The biomass containment structure of the type specified herein can be used to store biomass for long periods of time, even in the tropics. Once sealed within the structure, the biomass may be sterilized with a strong acid. This "pickling" procedure is facilitated by the agitation that may be developed through vacuum compaction and release of the vacuum. When the containment structure is composed principally of plastic or hydrocarbon film or sheeting, large volumes of biomass so treated may be stored at reduced cost.